A Simple Alternative Method to Estimate the Collapse Pressure of Flexible Pipes

2010 ◽  
Author(s):  
Victor Pinheiro Pupo Nogueira ◽  
Theodoro Antoun Netto
Keyword(s):  
Structural Integrity ◽  
Plastic Material ◽  
Numerical Models ◽  
Gas Production ◽  
Material Behavior ◽  
Flexible Pipe ◽  
Collapse Pressure ◽  
Operational Conditions ◽  
Alternative Method ◽  
Flexible Pipes

Offshore oil and gas production worldwide constantly moves to deeper water with increasing flexible pipe operational severity. Failure mechanisms, i.e., sequences of events which may lead to failure, are nowadays more likely to happen. Therefore, it is important to develop reliable numerical tools that can be used in the design stages or during service-life to assess the structural integrity of pipes under specific operational conditions. This work presents a methodology to develop simple finite element models capable to reproduce the behavior of structural layers of flexible pipes under hydrostatic pressure up to the onset of collapse. The models use beam elements and include contact between layers, nonlinear kinematics and material behavior. Different configurations were analyzed: carcass-only, and carcass plus pressure armor with dry and wet annular. The dependability of the numerical models is assessed in light of experimental tests on flexible pipes with 4 and 8 inch nominal internal diameters. Relevant geometric parameters and material properties of each specimen were measured and subsequently used in the models to reproduce the physical experiments. The metallic inner carcass and pressure armor layer manufacturing processes cause a high degree of stress-induced material anisotropy. Due to the inherent difficulty to determine the non-homogeneous elastic-plastic material behavior of the wires’ cross-sections, a novel alternative method was used to estimate their average stress-strain curves up to moderate strains (2%). Good correlation was obtained between experimental and numerical results. The applied methodology proved to be simple and yet efficient and reliable for the estimation of the collapse pressure of flexible pipes.

Development and Experimental Calibration of Numerical Model Based on Beam Theory to Estimate the Collapse Pressure of Flexible Pipes

2015 ◽  
Author(s):  
Jefferson Lacerda ◽  
Marcelo I. Lourenço ◽  
Theodoro A. Netto
Keyword(s):  
Structural Integrity ◽  
Oil And Gas ◽  
Numerical Models ◽  
Beam Theory ◽  
Gas Production ◽  
Operating Conditions ◽  
Flexible Pipe ◽  
Experimental Calibration ◽  
Collapse Pressure ◽  
Flexible Pipes

The constant advance of offshore oil and gas production in deeper waters worldwide led to increasing operational loads on flexible pipes, making mechanical failures more susceptible. Therefore, it is important to develop more reliable numerical tools used in the design phase or during the lifetime to ensure the structural integrity of flexible pipes under specific operating conditions. This paper presents a methodology to develop simple finite element models capable of reproducing the behavior of structural layers of flexible pipes under external hydrostatic pressure up to collapse. These models use beam elements and, in multi-layer analyses, include nonlinear contact between layers. Because of the material anisotropy induced by the manufacturing process, an alternative method was carried out to estimate the average stress-strain curves of the metallic layers used in the numerical simulations. The simulations are performed for two different configurations: one where the flexible pipe is composed only of the interlocked armor, and another considering interlocked armor and pressure armor. The adequacy of the numerical models is finally evaluated in light of experimental tests on flexible pipes with nominal internal diameters of 4 and 6 in.

Prediction of Burst in Flexible Pipes

2013 ◽  
Vol 135 (1) ◽  
Author(s):  
Alfredo Gay Neto ◽  
Clóvis de Arruda Martins ◽  
Celso Pupo Pesce ◽  
Christiano Odir C. Meirelles ◽  
Eduardo Ribeiro Malta ◽  
...  
Keyword(s):  
Internal Pressure ◽  
Cross Section ◽  
Plastic Material ◽  
Numerical Models ◽  
Fluid Pressure ◽  
Material Model ◽  
Flexible Pipe ◽  
Flexible Pipes ◽  
Equivalent Ring ◽  
Cross Section Profile

Usually when a large internal fluid pressure acts on the inner walls of flexible pipes, the carcass layer is not loaded, as the first internal pressure resistance is given by the internal polymeric layer that transmits almost all the loading to the metallic pressure armor layer. The last one must be designed to ensure that the flexible pipe will not fail when loaded by a defined value of internal pressure. This paper presents three different numerical models and an analytical nonlinear model for determining the maximum internal pressure loading withstood by a flexible pipe without burst. The first of the numerical models is a ring approximation for the helically rolled pressure layer, considering its actual cross section profile. The second one is a full model for the same structure, considering the pressure layer laying angle and the cross section as built. The last numerical model is a two-dimensional (2D) simplified version, considering the pressure layer as an equivalent ring. The first two numerical models consider contact nonlinearities and a nonlinear elastic-plastic material model for the pressure layer. The analytical model considers the pressure armor layer as an equivalent ring, taking into account geometrical and material nonlinear behaviors. Assumptions and results for each model are compared and discussed. The failure event and the corresponding stress state are commented.

Burst Prediction of Flexible Pipes

2010 ◽  
Author(s):  
Alfredo Gay Neto ◽  
Clo´vis de Arruda Martins ◽  
Celso Pupo Pesce ◽  
Christiano Odir C. Meirelles ◽  
Eduardo Ribeiro Malta ◽  
...  
Keyword(s):  
Numerical Model ◽  
Internal Pressure ◽  
Cross Section ◽  
Plastic Material ◽  
Numerical Models ◽  
Fluid Pressure ◽  
Material Model ◽  
Flexible Pipe ◽  
Flexible Pipes ◽  
Polymeric Layer

Usually, when a large internal fluid pressure acts on the inner walls of flexible pipes, the carcass layer is not loaded as the first internal pressure resistance is given by the internal polymeric layer. The internal polymeric layer transmits almost all that loading to the metallic pressure resistant layer, or pressure armor layer. This layer must then be designed to ensure that the flexible pipe will not fail when loaded by a defined value of internal pressure. The present paper presents three different numerical models and one simple analytical model for determining the maximum internal pressure loading for a flexible pipe. The aim is to avoid pipe burst. The first numerical model is a ring approximation for the helically rolled pressure layer, considering its cross section as built. A second one is a full model for the same structure, considering the pressure layer laying angle and the cross section as built. The third numerical model is a 2D simplified version, considering the pressure layer as an equivalent ring. The first two numerical models consider contact nonlinearities and a nonlinear elastic-plastic material model for the pressure layer. The failure event and the corresponding stress state are discussed. Assumptions for each model are compared and discussed, with comparative results.

A Continued Evaluation of the Role of Material Hardening Behavior for the NeT TG1 and TG4 Specimens

2014 ◽  
Author(s):  
David J. Dewees ◽  
Phillip E. Prueter ◽  
Seetha Ramudu Kummari
Keyword(s):  
Structural Integrity ◽  
Plastic Material ◽  
Critical Factor ◽  
Material Model ◽  
Standard Test ◽  
Material Behavior ◽  
Weld Residual Stress ◽  
Hardening Models ◽  
Elastic Plastic Material

Modeling of cyclic elastic-plastic material behavior (hardening) has been widely identified as a critical factor in the finite element (FE) simulation of weld residual stresses. The European Network on Neutron Techniques Standardization for Structural Integrity (NeT) Project has provided in recent years both standard test cases for simulation and measurement, as well as comprehensive material characterization. This has allowed the role of hardening in simulation predictions to be isolated and critically evaluated as never before possible. The material testing information is reviewed, and isotropic, nonlinear kinematic and combined hardening models are formulated and tested. Particular emphasis is placed on material model selection for general fitness-for-service assessments, as it relates to the guidance for weld residual stress (WRS) in flaw assessments of in-service equipment in Annex E of the FFS standard, API 579-1/ASME FFS-1.

Whistling of Pipes With Narrow Corrugations: Scale Model Tests and Consequences for Carcass Design

2013 ◽  
Author(s):  
Joachim Golliard ◽  
Stefan Belfroid ◽  
Erik Bendiksen ◽  
Casper Frimodt
Keyword(s):  
Prediction Model ◽  
Gas Production ◽  
Scale Model ◽  
Small Scale ◽  
Operational Conditions ◽  
Flexible Pipes ◽  
Cavity Opening ◽  
Flexible Risers ◽  
Onset Velocity ◽  
Operational Envelope

Pipes for gas production and transport with a corrugated inner surface, as used in flexible pipes, can be subject to Flow-Induced Pulsations when the flow velocity is larger than a certain velocity. This onset velocity is dependent on the geometry of the corrugations, the operational conditions and the geometry of the topside and subsea piping. In this paper, small-scale tests performed on corrugated tubes are reported. The tested geometries include both “classical” profiles, similar to the inner profile of agraff flexible risers, and profiles with less typical variations, such as narrower and/or deeper cavities, or irregular pitch. These tests were performed in order to evaluate the validity of a prediction model developed earlier for the onset of pulsations, for corrugated pipes with these kinds of atypical variations, which are found on a new type of carcass designs. The mechanism of Flow-Induced Pulsations in corrugated pipes is discussed, as well as the principle of the prediction model. The experimental results show that the validity of the model remains reasonable in most cases, except when the cavities are very narrow. In this case, the model becomes overly conservative. This limitation can be attributed to the fact that, for very narrow cavities, the cavity opening becomes too small compared to the boundary-layer momentum thickness, effectively destroying any instability of the shear layer. Furthermore, the shift towards higher frequencies of the acoustic source term due to narrower cavities, and the possible coupling with higher acoustic modes, is considered. The results of the analysis are used to evaluate the onset velocity and whistling behavior of a newly developed carcass design of flexible risers. A previous analysis has indicated that the particular geometry profile of the new design improves the whistling behavior by pushing the onset velocity outside the typical operational envelope of flexible risers. The analysis confirms that the new design will be less prone to whistling than flexible risers with classical agraff carcasses.

A KNN Based Collapse Methodology and Recent Qualification of Flexible Pipes in Deepwater Application

2020 ◽  
Author(s):  
Linfa Zhu ◽  
Victor Pinheiro Pupo Nogueira ◽  
Zhimin Tan
Keyword(s):  
Structural Characteristics ◽  
Design Guidelines ◽  
Flexible Pipe ◽  
Collapse Pressure ◽  
Collapse Strength ◽  
Flexible Pipes ◽  
Collapse Model ◽  
Testing Data ◽  
Collapse Prediction ◽  
Current Design

Abstract As the flexible pipe industry targets more on deepwater applications, collapse performance of flexible pipes becomes a key challenge due to the huge hydrostatic pressure during installation and service. The collapse strength of flexible pipes largely depends on the structural characteristics of carcass, pressure sheath and pressure armor layers. Therefore, the collapse prediction methodology involving a sound modeling of these layers is essential. Over the years, Baker Hughes have collected a large amount of collapse testing data. The prediction tool needs to be validated and calibrated against all the collapse tests for best accuracy. In this paper, the latest progress of the collapse prediction methodology and qualification tests are presented. A generalized collapse model was developed to predict the collapse pressure of flexible pipes. This model incorporates the advantages of both the weighted kNN regression technique and an analytical collapse model. It is able to reproduce the exact collapse pressure on the pipes tested and can predict the collapse pressure of other pipe designs not tested. As part of the qualification process, the capacity to prevent collapse must be demonstrated. Several flexible pipes were designed based on this generalized prediction methodology for deep water application, and pipe samples were manufactured using industrial production facilities for collapse tests. The results show that flexible pipes following current design guidelines are suitable for deepwater applications.

Flexible Pipes: Influence of the Pressure Armor in the Wet Collapse Resistance

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
Alfredo Gay Neto ◽  
Clóvis de Arruda Martins
Keyword(s):  
Three Dimensional ◽  
External Pressure ◽  
Flexible Pipe ◽  
3D Fem ◽  
Collapse Pressure ◽  
Flexible Pipes ◽  
Polymeric Layer ◽  
Set Up ◽  
3D Finite Element Method ◽  
Ring Approximation

When submitted to high external pressure, flexible pipes may collapse. If the external sheath is damaged, all the external pressure is directly applied on the internal polymeric layer that transmits the loading to the carcass layer, which can fail due to this effect, leading to wet collapse. This failure mode must be taken into account in a flexible pipe design. A model can be set up neglecting the influence of the pressure armor, but this assumption may underestimate the wet collapse pressure value. This work aims to include the pressure armor effect in the numerical prediction of wet collapse. The main contribution of the pressure armor to the flexible pipe resistance to collapse is to be a constraint to the radial displacement of the carcass and the internal polymeric layers. Two models were developed to find the wet collapse pressure in flexible pipes. A first study was done using a ring approximation three-dimensional (3D) finite element method (FEM) model. Comparisons are made with more simplified models using a 3D FEM equivalent ring approximation. The aim is to clarify the mechanical behavior of the pressure armor in the wet collapse scenario. Parametric studies of initial ovalization of carcass and initial gaps and interference between polymeric layer and pressure armor are made and discussed.

On Determination of Acceptable Safety Class in Design of Pipe-In-Pipe (PIP) Systems

2014 ◽  
Author(s):  
Soheil Manouchehri ◽  
Guillaume Hardouin ◽  
David Kaye ◽  
Jason Potter
Keyword(s):  
Failure Modes ◽  
Structural Integrity ◽  
Oil And Gas ◽  
Gas Production ◽  
Point Of View ◽  
Insulation Material ◽  
Limit States ◽  
Oil And Gas Production ◽  
Operational Conditions ◽  
Outer Pipe

Pipe-In-Pipe (PIP) systems are increasingly used in subsea oil and gas production where a low Overall Heat Transfer Coefficient (OHTC) is required. A PIP system is primarily composed of an insulated inner pipe which carries the production fluid and an outer pipe that protects the insulation material from the seawater environment. This provides a dry environment within the annulus and therefore allows the use of high quality dry insulation system. In addition, from a safety point of view, it provides additional structural integrity and a protective barrier which safeguards the pipeline from loss of containment to the environment. Genesis has designed a number of PIP systems in accordance with the recognized subsea pipeline design codes including DNV-OS-F101 [1]. In section 13 F100 of the 2013 revision, a short section has been included in which PIP systems are discussed and overall design requirements for such systems are provided. It has also been stated that the inner and outer pipes need to have the same Safety Class (SC) unless it can be documented otherwise. This paper looks at the selection of appropriate SC for the outer pipe in a design of PIP systems based on an assessment of different limit states, associated failure modes and consequences. Firstly, the fundamentals of selecting an acceptable SC for a PIP system are discussed. Then, different limit states and most probable failure modes that might occur under operational conditions are examined (in accordance with the requirements of [1]) and conclusions are presented and discussed. It is concluded that the SC of the outer pipe of a PIP system may be lower than that of the inner pipe, depending on the failure mode and approach adopted by the designer.

Repair Techniques for Flexible Pipe External Sheath

2008 ◽  
Author(s):  
T. A. Netto ◽  
J. M. Touc¸a ◽  
M. Ferreira ◽  
V. Gonc¸alez ◽  
R. Marnet
Keyword(s):  
Sea Level ◽  
Structural Integrity ◽  
Annular Region ◽  
Annular Space ◽  
Flexible Pipe ◽  
Flexible Pipes ◽  
Cutting Out ◽  
Inspection Techniques ◽  
Repair Techniques

During installation or service, the external sheath of flexible pipes can suffer damages that may result in loss of sealing and exposure of the annular region to the external environment. Additionally, visual inspection of the armor layers is sometimes necessary to assess their structural integrity. Such procedure requires cutting out a small segment (window) of the external sheath. One of the most effective inspection techniques to detect problems in the topside relief valves, damages on the external sheath, or pressure barrier failure is the surface monitoring of the pressure in the annular region. Therefore, in the event of sheath damage or inspection windows, in situ repair techniques that guarantee the recovery of its sealing properties are important, particularly in the regions above sea level and water depths usually up to 30 meters. When the pipes are below this level, repairs are in general done on board of an installation vessel. Due to the inherent complexities of each region, specific repair techniques have been developed by PETROBRAS to date. Nevertheless, these techniques do not guarantee the annular space sealing, therefore hampering pressure monitoring. The objective of this work was to develop an external sheath repair technique using light, resistant, and easy-to-install materials for the areas above sea level and small depths (up to 30 m) capable to provide the necessary sealing for annular space monitoring.

A Comparative Wet Collapse Buckling Study for the Carcass Layer of Flexible Pipes

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
Alfredo Gay Neto ◽  
Clóvis de Arruda Martins
Keyword(s):  
Analytical Model ◽  
Numerical Models ◽  
External Pressure ◽  
Plastic Layer ◽  
Plastic Behavior ◽  
Flexible Pipe ◽  
Equivalent Thickness ◽  
Collapse Pressure ◽  
Ring Model ◽  
Collapse Behavior

When there is a failure on the external sheath of a flexible pipe, a high value of hydrostatic pressure is transferred to its internal plastic layer and consequently to its interlocked carcass, leading to the possibility of collapse. The design of a flexible pipe must predict the maximum value of external pressure the carcass layer can be subjected to without collapse. This value depends on the initial ovalization due to manufacturing tolerances. To study that problem, two numerical finite element models were developed to simulate the behavior of the carcass subjected to external pressure, including the plastic behavior of the materials. The first one is a full 3D model and the second one is a 3D ring model, both composed by solid elements. An interesting conclusion is that both the models provide the same results. An analytical model using an equivalent thickness approach for the carcass layer was also constructed. A good correlation between analytical and numerical models was achieved for pre-collapse behavior but the collapse pressure value and post-collapse behavior were not well predicted by the analytical model.

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